In aircrafts, but also in other vehicles such as collective transport vehicles like buses or trains or in theatres or the like, there are seat arrangements wherein two neighboring seats share an armrest. Especially in the economy class of aircrafts a “fight for the armrest” is often a cause for discomfort of the passengers.
The design of a seat armrest has usually fixed dimension including the armrest width. Today an aircraft cross section is designed to accommodate multiple seat blocks. The space offered to the passenger in transversal direction is often given by the width between armrests, which airlines want to maximize, by reducing aisle or armrest width.